Method and apparatus for sensing nitroaromatics

ABSTRACT

The subject invention pertains to a method and apparatus for sensing nitroaromatics. The subject invention can utilize luminescent, for example fluorescent and/or electroluminescent, aryl substituted polyacetylenes and/or other substituted polyacetylenes which are luminescent for sensing nitroaromatics. In a specific embodiment, the subject invention can utilize thin films of fluorescent and/or electroluminescent aryl substituted polyacetylenes and/or other substituted polyacetylenes which are fluorescent and/or electroluminescent. In a specific embodiment, the fluorescence from thin films of fluorescent, substituted polyacetylene, such as—poly-[1-phenyl-2-(4-trimethylsilylphenyl)ethyne] (PTMSDPA) is strongly quenched by the vapors of a variety of nitroaromatic compounds present at levels ranging from parts-per-million to parts-per-billion in air.

CROSS-REFERENCE TO RELATED APPLICATION(s)

The present application claims the benefit of U.S. ProvisionalApplication Serial No. 60/329,070, filed Oct. 12, 2001, which is herebyincorporated by reference herein in its entirety, including any figures,tables, nucleic acid sequences, amino acid sequences, or drawings.

The subject invention was made with government support under a researchproject supported by Defense Advanced Research Projects Agency (grant #DAAD 19-00-1-0002).

BACKGROUND OF INVENTION

Conjugated polymers have received considerable attention as the activematerials in fluorescence-based chemical sensors because of their highsensitivity to a variety of solution- and vapor-phase analytes. Theresponse characteristics of a thin-film polymer fluorescence sensordepend strongly on a number of factors including the permeability of theanalyte in the polymer, and the strength of the chemical (or physical)interaction between the analyte and the photoactive polymer, wherepermeability (P) is the product solubility (S) and diffusivity (D) of ananalyte in a polymer, i.e., P=S*D. Recently, it has been demonstratedthat by using a sterically demanding pentiptycene moiety it is possibleto increase the permeability of a highly fluorescentpoly(phenyleneethynylene) film thereby increasing the response of thematerial to vapor-phase analytes. The bulky pentiptycene moiety isbelieved to create molecular-scale channels which provide pathways forthe analyte molecules to diffuse into the polymer and readily interactwith the electron-rich π-conjugated system. The resulting increase inpermeability of the pentiptycene-substituted poly(phenyleneethynylene)film can allow the analyte to quench the polymer's fluorescence morerapidly and efficiently compared to similar polymers that lack thesterically-demanding pentiptycene group. Others have demonstrated thatdoping a surfactant into a film of a fluorescent conjugatedpolyelectrolyte considerably improves the film's response to neutralanalyte molecules. The surfactant is believed to improve thefluorescence response by increasing the solubility (sorption) of theneutral analyte in the film.

BRIEF SUMMARY

The subject invention pertains to a method and apparatus for sensingnitroaromatics. The subject invention can utilize luminescent, forexample fluorescent and/or electroluminescent, aryl substitutedpolyacetylenes and/or other substituted polyacetylenes which areluminescent for sensing nitroaromatics. In a specific embodiment, thesubject invention can utilize thin films of fluorescent and/orelectroluminescent aryl substituted polyacetylenes and/or othersubstituted polyacetylenes which are fluorescent and/orelectroluminescent. In a specific embodiment, the subject inventioninvolves a method of using the disubstituted polyacetylene PTMSDPA todetect the presence of nitroaromatic vapors. The subject invention alsorelates to nitroaromatic vapor sensors incorporating fluorescent and/orelectroluminescent aryl substituted polyacetylenes and/or othersubstituted polyacetylenes which are fluorescent andor/electroluminescent. In a specific embodiment, the subjectnitroaromatic sensor can utilize disubstituted polyacetylene PTMSDPAthin films. The subject thin films can exhibit fluorescence that isstrongly quenched by nitroaromatic vapors. Alternatively, the subjectthin films can exhibit electroluminescence created by the application ofan electric field across the thin film. In this case, theelectroluminescence can be quenched by exposure of the thin films to thetarget nitroaromatic compound.

In addition, the subject thin films can be used as the active materialin a device, for example a diode type device, which produces anelectrical signal, wherein exposure of the active material to the targetnitroaromatic compound alters the electrical signal of the device.Preferably, the electrodes of such a device would allow the ambientatmosphere to reach the active material. For example, porous electrodes,interdigitated electrodes, or electrodes having channels can be used.

In another embodiment, particles of the fluorescent aryl substitutedpolyacetylenes or other fluorescent substituted polyacetylenes can bepositioned in an environment to be tested and appropriate light shone onthe particles such that particles located near a source of nitroaromaticcompound, for example a landmine, would not fluoresce to the degree ofparticles not near such sources or nitroaromatic compounds. Preferably,the subject films or particles have thicknesses or mean diameters ofless than 100 nm. The physical mechanism for the quenching process isbelieved to involve CT complexes that are formed, for example, betweenthe nitroaromatic acceptors and the electron rich PTMSDPA polymer chain.PTMSDPA has a unique combination of properties, including high vaporpermeability and strong fluorescence, which are valuable for use inoptical sensors. Sensors in accordance with the subject invention candetect the presence of nitroaromatic vapors upon the quenching ofphotoluminescence, for example fluorescence and/or electroluminescenceproduced by films or particles of disubstituted polyacetylene PTMSDPA.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a fluorescence microscope image of a 7 nm thick PTMSDPAfilm having an image size of 385×308 μm, where white scale bar is 100 μmlong and color scale ranges from 900–10,000 counts.

FIG. 1B shows an AFM image of a 7 nm thick PTMSDPA film having an imagesize of 450 nm×450 nm.

FIG. 2 shows the fluorescence from a 7 nm thick PTMSDPA film at varioustimes following introduction of solid 2,6-DNT to the fluorescencecuvette, where the inset shows the fluorescence intensity as a functionof exposure time.

FIG. 3 shows PTMSDPA fluorescence intensity as a function of exposuretime to 2,4-DNT vapor, where the legend indicates the thickness of thePTMSDPA films.

FIG. 4 illustrates fluorescence quenching (% decrease of the initialintensity) of 3 nm PTMSDPA films by various analytes, where quenching %was determined after the film was exposed to the analyte vapor for 20min at 298 K.

FIG. 5 shows the structure of PTMSDPA.

FIG. 6 shows a schematic of a chemical explosives sensor based on PTMSP.

DETAILED DISCLOSURE

The subject invention pertains to a method and apparatus for detectingnitroaromatic compounds. A specific embodiment of the subject inventioncan utilize changes in the luminescence emitted from luminescent arylsubstituted polyacetylenes and/or other luminescent substitutedpolyacetylenes to detect the presence of nitroaromatics. In a furtherembodiment, the subject invention can utilize changes in theluminescence emitted from fluorescent aryl substituted polyacetylenesand/or other fluorescent substituted polyacetylenes to detect thepresence of nitroaromatics. In another specific embodiment, the subjectinvention can utilize changes in electroluminescence emitted fromelectroluminescent aryl substituted polyacetylenes and/or otherelectroluminescent substituted polyacetylenes to detect the presence ofnitroaromatics preferably, substituted polyacetylenes with large gaspermeability are used. Examples of polymers which can be utilized withthe subject invention include poly-(1-trimethylsilylpropyne) (PTMSP) andpoly-[1-phenyl-2-(4-trimethylsilylphenyl)ethyne] (PTMSDPA). PTMSP hasthe highest fractional free volume (0.29) and gas permeability of allknown polymers, while PTMSDPA displays exceptionally high permeabilityand high fractional free volume (0.26). In addition to being highlypermeable, like many other bis-aryl substituted polyacetylenes PTMSDPAis strongly fluorescent. In a specific embodiment, PTMSDPA can be usedin the fabrication of a thin-film and/or particle based fluorescentsensor for vapors of neutral analytes. Nitroaromatic compounds areweakly volatile and are strong quenchers of the fluorescence of electronrich chromophores. The detection of nitroaromatic vapors can include thedetection of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT),as these materials are the primary constituents of the explosives usedin many land mines.

The luminescent aryl substituted polyacetylenes and/or other luminescentsubstituted polyacetylenes utilized in accordance with the subjectinvention can have a variety of shapes, such as thin films, particles,and/or fibers. In specific embodiments, the thin films, particles,and/or fibers utilized in accordance with the subject invention can havethicknesses, mean diameters, and mean diameters of less than about 1 μm,respectively. In a further specific embodiment, the thicknesses, meandiameters, and mean diameters of the thin films, particles, and/orfibers can be less than about 100 nm, respectively. In a furtherspecific embodiment, the thicknesses, mean diameters and mean diametersof the thin films, particles, and/or fibers, can be less than about 10nm, respectively.

Various excitation sources can be utilized to cause the photoluminescentaryl substituted polyacetylenes and/or other luminescent substitutedpolyacetylenes to luminesce, for example to fluoresce and/orelectroluminesce. Such excitation sources can include, for example,lasers, LED's, and electrodes to apply a voltage across theelectroluminescent material, and/or other excitation sources known inthe art.

Various means for monitoring the luminescence emitted from theluminescent aryl substituted polyacetylene and/or other luminescentsubstituted polyacetylense can be used, such as a human eye,photomultiplier, solid state detector, charge coupled device (CCD), orother photodetecting means known in the art.

The polyacetylenes utilized in the methods and devices in the subjectinvention can be substituted, for example, with an aromatic orheteroaromatic moiety, or with a chemical group that contains anaromatic or heteroaromatic moiety. In a specific embodiment, thepolyacetylenes utilized in accordance with the subject invention can besubstituted, for example with a moiety selected from the groupconsisting of: aryloxycarbonyl arylcarbonyloxy, heteroaryl-oxycarbonyl,and heteroarylcarbonyloxy each of which is, optionally, substituted withC₁₋₁₀ alkyl, CN, COOH, NO₂, NH₂, SO₂₋₄, C₁₋₂₀ heteroalkyl, C₂₋₂₀alkenyl, alkynyl, akynyl-aryl, alkynyl-heteroaryl, aryl, C₁₋₂₀alkyl-aryl, C₂₋₂₀ alkenyl-aryl, heteroaryl, C₁₋₂₀ alkyl-heteroaryl,C₂₋₂₀ alkenyl-heteroaryl, cycloalkyl, heterocycloalkyl, C₁₋₂₀alkyl-heteroycloalkyl, and C₁₋₂₀ alkyl-cycloalkyl, any of which may be,optionally, substituted with a moiety selected from the group consistingof C₁₋₆ alkyl, halogen, OH, NH₂, CN, NO₂, COOH, or SO₂₋₄.

In other embodiments, the substituted carboxylic group can besubstituted with a moiety selected from the group consisting of C₁₋₁₀alkyl, CN, COOH, NO₂, NH₂, SO₂₋₄, C₁₋₂₀ heteroalkyl, C₂₋₂₀ alkenyl,alkynyl, akynyl-aryl, alkynyl-heteroaryl, aryl, C₁₋₂₀ alkyl-aryl, C₂₋₂₀alkenyl-aryl, heteroaryl, C₁₋₂₀ alkyl-heteroaryl, C₂₋₂₀alkenyl-heteroaryl, cycloalkyl, heterocycloalkyl, C₁₋₂₀alkyl-heteroycloalkyl, and C₁₋₂₀ alkyl-cycloalkyl, any of which may be,optionally, substituted with a moiety selected from the group consistingof C₁₋₆ alkyl, halogen, OH, NH₂, CN, NO₂, COOH, or SO₂₋₄. Exemplaryheterocyclic groups include, but are not limited to, morpholine,triazole, imidazole, pyrrolidine, piperidine, piperazine, pyrrole,dihydropyridine, aziridine, thiazolidine, thiazoline, thiadiazolidine,and thiadiazoline.

Vapor-phase nitroaromatic compounds can quench the fluorescence of thinfilms of PTMSDPA when PTMSDPA thin films are exposed to such vapor-phasenitroaromatic compounds. FIG. 4 illustrates the quenching results of aseries of nitroaromatics which can quench the fluorescence of PTMSPDPAstrongly and selectively. The nitroaromatics addressed in FIG. 4 include1,4-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, and1,3-dinitrobenzene. The nitroaromatic quenching phenomenon is believedto arise from charge transfer (CT) complex formation between theelectron-rich PTMSDPA backbone and the electron poor nitroaromatic. Therapid response of the material is clearly related to its highpermeability and fractional free volume which allows the vapor phasenitroaromatic molecules to penetrate into the film rapidly.

In a specific embodiment, PTMSDPA can be produced by a variety ofmethods. PTMSDPA can be, for example, synthesized by polymerization of1-phenyl-2-(4-trimethylsilylphenyl)ethyne, which can be preparedaccording to the procedure described in Tsuchihara, K.; Masuda, T.;Higashimura, T. J. Am. Chem. Soc. 1991, 113, 8548–8549, which isincorporated herein by reference. Polymerization can be carried out byuse of a variety of catalysts, for example with a TaCl₅/n-Bu₄Sn catalystas described in Tsuchihara, K.; Masuda, T.; Higashimura, T.Macromolecules 1992, 25, 581–5820; and in Teraguchi, M.; Masuda, T. J.Poly. Sci. A Poly. Chem. 1998, 36, 2721–2725, both of which areincorporated herein by reference.

PTMSDPA can be synthesized by polymerization of1-phenyl-2-(4-trimethylsilylphenyl)ethyne using a TaCl₅/n-Bu₄Sn catalystin accordance with the Tsuchihara K.; Masuda T.; Higashimura, T. J. Am.Chem. Soc. (1991) 113, 8548–8549, and Tsuchihara, K.; Masuda, T.;Higashimura, T. Macromolecules 1992, 25, 5816–5820 (1992), which areherein incorporated by reference. The molecular weight of PTMSDPAproduced in this way was determined on a Rainin Dynamax HPLC that wasequipped with two PLgel 5 μm Mixed-D size exclusion columns (300×7.5 mm,Polymer Labs) and a UV absorbance detector operating at 260 nm. The GPCwas calibrated using polystyrene standards (Polymer Laboratories). Filmsof PTMSDPA were spin-cast from toluene solution onto borosilicate glassmicroscope cover slides at a spin rate of 2000 rpm. The films were driedunder vacuum at room temperature overnight before the experiments werecarried out. The concentration of the PTMSDPA/toluene solution wasadjusted to vary the film thickness. A concentration of 0.7 mg-mL⁻¹produced a film of 3 nm thickness. The thickness of the ultrathin filmswas estimated by measuring the film's absorbance at 425 nm. Theabsorbance versus thickness calibration plot was constructed bymeasuring the absorbance of films of known thicknesses ranging from50–100 nm. The thickness of these films was determined by profilometryon a Dektak 3030 profilometer. Atomic Force Microscopy (AFM) wasperformed under ambient conditions with a Nanoscope III (DigitalInstruments, Santa Barbara, Calif.) operating in tapping mode usingsilicon nitride tips. The fluorescence microscope system consisted of aninverted microscope platform (Olympus, model IX 70) fitted with a 100 WHg source (USH-102DH) and a CCD camera (Princeton, RTE 1300×1030)mounted to the side port. Fluorescence microscopy was conducted with ablue-violet modular filter cube (Chroma Technology, excitation 425 nm,40 nm bandpass; 475 nm dichroic splitter). The fluorescence emission wasimaged through a 475 nm long pass filter (Chroma Technology).

Fluorescence spectra were measured on a SPEX Fluorolog-2 or on aspectrometer consisting of an ISA-SPEX Triax 180 spectrograph equippedwith a LN2 cooled CCD detector (Hamamatsu CCD, 1024×64 pixels). Duringfluorescence measurements the polymer films were contained in sealedquartz cuvettes. For quenching studies, the solid analyte was added attime=0 and then the cuvette was sealed to allow the solid-vaporequilibrium to be established. Fluorescence spectra were recorded atintervals after addition of the analyte. Absorption spectra wereobtained on a Cary-100 UV-visible spectrometer. Fluorescence lifetimeswere measured using a PRA time-correlated single photon countinginstrument that used a 405 nm pulsed laser diode with 800 ps pulse width(nano-LED, IBH Co., Glascow, UK) as an excitation source and thefluorescence wavelength was selected by using a 550 nm (10 nm bandwidth)interference filter.

PTMSDPA can be synthesized by polymerization of1-phenyl-2-(4-trimethylsilylphenyl)ethyne using a TaCl₅/n-Bu₄Sncatalyst. The polymerization reaction is facile and proceeds in highyield making it possible to produce multi-gram quantities of PTMSDPA inone polymerization reaction. GPC analysis of the PTMSDPA sample producedin this way indicate that the material has M_(n)=293,000 (PDI=1.6). Thepolymer has good solubility in THF, toluene and chlorinatedhydrocarbons, and solutions can be cast to form films having outstandingmechanical properties (indeed, free-standing films of the material canbe easily prepared).

As noted above, previous studies demonstrate that PTMSDPA is highlypermeable to light gases (i.e., N₂, O₂ and H₂) and hydrocarbon vapors.The high permeability has been ascribed to the polymer's largefractional free volume and interconnected “channels” that allow smallmolecules to rapidly diffuse within the matrix. In order to explore themorphology of ultrathin films of PTMSDPA similar to those used in thefluorescence sensor work described below, we used fluorescencemicroscopy and tapping-mode AFM to image the surface of 7 nm thick filmsof the polymer that were spin-coated from toluene. FIG. 1A illustrates afluorescence microscope image of a typical region of the film (385×308μm). The image is quite uniform—with the exception of a few pointdefects, the film features a very homogeneous fluorescence intensity.Thus, on the length scale accessible with optical microscopy the PTMSDPAfilms are uniform. In order to examine the film morphology with higherspatial resolution we examined the same film using tapping mode AFM. Atypical AFM image of a PTMSDPA film is illustrated in FIG. 1B; analysisof this image reveals that the surface exhibits an RMS roughness of 0.5nm. The AFM imaging experiments indicate that spin-coated films ofPTMSDPA feature a continuous but somewhat “porous” structure having alength scale on the order of 10–20 nm. The porous surface morphologythat is imaged by AFM may reflect the relatively porous structure of thepolymer bulk that is caused by the inability of the rigid polyacetylenechains to pack in the solid. This porous structure allows the bulk ofthe film to equilibrate rapidly with vapor-phase analytes (see below).

In toluene solution PTMSDPA (c=50 μM) features absorption bands at 430nm (ε=4630 M⁻¹cm⁻¹) and 370 nm (ε=4440 M⁻¹cm⁻¹, ε values computed basedon repeat unit molecular mass) and a broad fluorescence band withλ_(max)=520 nm. The polymer's fluorescence is relatively efficient(φ=0.25) and very short-lived (τ<50 ps). These features are verycharacteristic of bis-aryl substituted polyacetylenes. The low-energyabsorption band of a 7 nm thick film of PTMSDPA is slightly blue-shiftedfrom its solution value (λ_(max) ^(film)=423 nm) and the fluorescence isslightly red-shifted (λ_(max) ^(film)=533 nm). These features areconsistent with the existence of interchain aggregates in the solidmaterial. Nevertheless, the fluorescence from the polymer film is verystrong and it is easily detected by eye when the material is illuminatedwith a 7 W near-UV handlamp.

FIG. 2 illustrates fluorescence spectra of a 7 nm thick spin-castPTMSDPA film as a function of time following the addition of a crystalof solid 2,6-dinitrotoluene (2,6-DNT) to the cuvette containing thefilm. This data shows that the PTMSDPA fluorescence intensity decreasessignificantly with increasing time of exposure to the 2,6-DNT. As shownin the inset of FIG. 2, the fluorescence intensity drops quickly withinthe first 2 minutes after addition of 2,6-DNT and then it decreases moreslowly until attaining stable value that is ≈10% of the unquenchedintensity. The rate by which the film's fluorescence is quenched isapparently determined by the sublimation rate of the 2,6-DNT and/or bythe rate at which the vapor of the analyte permeates into the polymerfilm. The fluorescence maximum and bandshape is unchanged in thepresence of the 2,4-DNT, which indicates that the interaction betweenthe electron poor nitroaromatic and the electron rich polyacetylene doesnot afford emissive (exciplex) states. Although the quenching isreversible, the fluorescence recovers more slowly than the quenchingdevelops. For example, a 3 nm thick film that had been exposed to2,6-DNT exhibited >90% recovery of the initial fluorescence intensitywhen it was allowed to stand in air for approximately 1 hr. The recoverytime can be decreased by purging with dry N₂ gas. For example, the 90%recovery time was decreased to approximately 10 min when the sample wasplaced in a vial that was being gently purged with dry N₂ gas.

The fact that the rate by which the nitroaromatic permeates into theconjugated polymer film is important in determining the rate of thefluorescence quenching process is established by a study of thequenching of a series of PTMSP films of varying thickness by2,4-dinitrotoluene (2,4-DNT). FIG. 3 illustrates the influence of filmthickness on the rate at which 2,4-DNT quenches the PTMSDPAfluorescence. It is clear that the rate of the quenching processincreases with decreasing film thickness. For an 80 nm thick film, thefluorescence decreases to 50% of its initial value in≈200 s (i.e.,t_(50%)=200 s); however, for a 3 nm thick film the 50% quenching levelis reached in less than 20 s (t_(50%)=20 s). Assuming that thesublimation rate is the same in the four 2,4-DNT quenching ratemeasurements, then it appears that the parameter responsible for theobserved difference in fluorescence quenching arises from the effect offilm thickness on the rate by which the nitroaromatic permeates into thefilm. If diffusion of the nitroaromatic into the film is the ratedetermining step for fluorescence quenching, it is expected that a plotof (fluorescence intensity)⁻¹ vs. (time)^(−1/2) will be linear. However,a such plot constructed using the data shown in FIG. 3 is not linear.The deviation from linearity may arise because the concentration of thenitroaromatic at the air-film interface is increasing during thetimescale of the experiments.

Additional evidence that the permeation of the analyte in the PTMSDPAfilm is the most important parameter in determining the fluorescencequenching response time is provided by a study of the time dependence ofthe fluorescence intensity from a PTMSDPA film for a series ofnitroaromatics. Table 1 summarizes the results of a series ofexperiments where the fluorescence intensity from a 3 nm thick spin-castPTMSDPA film is monitored as a function of time after being exposed tothe vapors of four different nitroaromatic compounds. This data showsthat the t_(50%) response time for the fluorescence quenching processdecreases along the series 1,4-DNB>>2,6-DNT>1,3-DNB>>4-NT (see footnoteto Table 1 for acronym definitions). Interestingly, the response timecorrelates strongly with the vapor pressure of the nitroaromatic, i.e.,t_(50%) decreases as the analyte's vapor pressure increases. A similardependence of the quenching response time on analyte vapor pressure wasreported by Yang and Swager in their study of pentiptycene-containingpoly-(phenyleneethynylene)s in Yang, J.-S.; Swager, T. M. J. Am. Chem.Soc. 1998, 120, 11864–11873, who concluded that permeation of thenitroaromatic vapor into the film was important in establishing theresponse time of the sensor film.

TABLE 1 Fluorescence Quenching Response Times^(a) Quencher^(b) VaporPressure/ppm in air^(c) t_(50%)/s^(d) 1,4-DNB 0.034 880 2,6-DNT 0.74 481,3-DNB 1.18 21 4-NT 210 10 ^(a)3 nm PTMSDPA film. ^(b)1,4-DNB =1,4-dinitrobenzene; 2,6-DNT = 2,6-dinitrotoluene; 1,3-DNB =1,3-dinitrobenzene; 4-NT = 4-nitrotoluene. ^(c)From ref. ³¹ ^(d)t_(50%)is the time required for the PTMSDPA fluorescence intensity to decreaseby 50%.

While the response time of the PTMSDPA thin film fluorescence sensorvaries strongly with analyte vapor pressure, in general the fluorescenceresponse reaches equilibrium in less than 20 min. FIG. 4 shows thequenching response of 3 nm thick PTMSDPA films to various analytes att=20 min after exposure to the analyte's vapor. This presentation showsthat all of the nitroaromatic compounds tested elicit a significantquenching response from the PTMSDPA film. Interestingly, however, otheraromatic compounds such as chloranil, 1,4-dimethoxybenzene (1,4-DMB) and1,2-dimethoxybenzene (1,2-DMB) give rise to very little quenching (or inthe case of 1,2-DMB lead to a slightly enhanced fluorescence intensity).These observations imply that PTMSDPA's quenching response is selectivefor nitroaromatic compounds. Furthermore, the data support the premisethat the mechanism for the fluorescence quenching is charge transfer(CT) complex formation between the electron-rich PTMSDPA chains and theelectron poor nitroaromatic residues. It is surprising that chloranil isa poor quencher, despite the fact that it has a relatively high vaporpressure and is a very good electron acceptor. This suggests thatspecific chemical interactions between the PTMSDPA and thenitroaromatics may be important in determining the strong fluorescencequenching response that is observed.

FIG. 5 shows the structure for PTMSDPA, which can be incorporated withspecific embodiments of the subject invention.

FIG. 6 illustrates a specific embodiment of a detection apparatus inaccordance with the subject invention. In this embodiment, a PTMSPsensor film is positioned to receive excitation illumination from anexcitation source. In the embodiment shown in FIG. 6, the excitationsource is a GaN 430 nm, 100 mW LED and the PTMSP sensor film ispositioned adjacent to the output of the LED. The PTMSP sensor film isalso positioned to be exposed to a volume of gaseous fluid in which oneor more nitroaromatics may be present. In the embodiment, a forcedgaseous flow of the volume of gaseous fluid in which one or morenitroaromatics may be present is delivered onto the surface of the PTMSPsensor film. A detector is positioned to measure the luminescenceemmitted from the PTMSP sensor film in a wavelength range correspondingto fluorescence from the PTMSP sensor film resulting from the excitationof the film by the LED. In the embodiment, shown in FIG. 6, the detectormeasures the luminescence emitted from the PTMSP sensor film whichpasses through a 550 nm bandpass filter, thus measuring the luminescenceemitted by the film at wavelengths of about 550 nm. Detection ofreduction in luminescence at wavelength of about 550 nm emitted from thefilm is an indication of the presence of one or more introaromatics inthe volume of gaseous fluid.

1. A method of detecting the presence of a nitroaromatic, comprising thesteps of: (a) exposing a luminescent bis-aryl substituted polyacetyleneto a volume of a gaseous fluid; (b) monitoring the amount ofluminescence emitted from the luminescent bis-aryl substitutedpolyacetylene, and (c) monitoring a level of luminescence emitted fromthe luminescent bis-aryl substituted polyacetylene to determine thepresence of a nitroaromatic in the volume of gaseous fluid.
 2. Themethod according to claim 1, wherein the luminescent bis-arylsubstituted polyacetylene is fluorescent.
 3. The method according toclaim 1, wherein the luminescent bis-and substituted polyacetylene iselectroluminescent.
 4. The method according to claim 1, wherein afractional free volume of said bis-aryl substituted polyacetylene is0.26.
 5. The method according to claim 1, wherein said monitoring stepcomprises a user visually monitoring the amount of luminescence emittedfrom the luminescent bis-aryl substituted polyacetylene.
 6. The methodaccording to claim 2, further comprising the steps of: exposing thefluorescent bis-aryl substituted polyacetylene to excitationillumination of a wavelength which causes fluorescence from thefluorescent bis-aryl substituted polyacetylene, wherein said monitoringstep comprises monitoring the amount of fluorescence emitted from thefluorescent bis-aryl substituted polyacetylene.
 7. The method accordingto claim 3, further comprising the steps of: exposing theelectroluminescent bis-aryl substituted polyacetylene to an electricfield which causes electroluminescence from the electroluminescentbis-aryl substituted polyacetylene, wherein said monitoring stepcomprises monitoring the amount of electroluminescence emitted from theelectroluminescent bis-aryl substituted polyacetylene.
 8. The methodaccording to claim 1, wherein the luminescent bis-aryl substitutedpolyacetylene comprisespoly-[1-phenyl-2-(4-trimethylsilylphenyl)ethyne].
 9. The methodaccording to claim 2, wherein the fluorescent bis-aryl substitutedpolyacetylene comprises polyacetylene comprisespoly-[1-phenyl-2-(4-trimethylsilylphenyl)ethyne].
 10. The methodaccording to claim 1, wherein the nitroaromatic is in the vapor-phase.11. The method according to claim 1, wherein the nitroaromatic isselected from the group consisting of 1,4-dinitrobenzene,2,4-dinitrotoluene, 2,6-dinitroluene, 1,3-dinitrobenzene,4-nitrotoluene, and 2,4,6-trinitrotoluene.
 12. The method according toclaim 1, wherein the luminescent bis-aryl substituted polyacetylene is apolymer film.
 13. The method according to claim 12, wherein the polymerfilm is less than 1 micron thick.
 14. The method according to claim 12,wherein the polymer film is less than 100 nanometers thick.
 15. Themethod according to claim 12, wherein the thickness of the polymer filmis within the range of 3 nanometers to 80 nanometers.
 16. The methodaccording to claim 1, wherein the polymer film is less than 10nanometers thick.
 17. The method according to claim 1, wherein theluminescent bis-aryl substituted polyacetylene is an active material ina device which produces an electrical signal, wherein said monitoringstep comprises monitoring the electrical signal.
 18. The methodaccording to claim 1, wherein the luminescent bis-aryl substitutedpolyacetylene is in a physical form selected from the group consistingof particles and fibers.
 19. The method according to claim 18, whereinthe mean diameter of the particles is less than 100 nm.
 20. The methodaccording to claim 18, wherein the mean diameter of the fibers is lessthan 100 nm.
 21. The method according to claim 1, wherein saidmonitoring step comprises monitoring the amount of luminescence emittedfrom the luminescent bis-aryl substituted polyacetylene with amonitoring means selected from the group consisting of an eye, aphotomultiplier, a solid state detector and a charge-couple device(CCD).
 22. The method according to claim 6, wherein exposing thefluorescent bis-aryl substituted polyacetylene to excitationillumination comprises exposing the fluorescent bis-aryl substitutedpolyacetylene to excitation illumination with an illumination meansselected from the group consisting of a laser and an LED.
 23. The methodaccording to claim 1, wherein the luminescent bis-aryl substitutedpolyacetylene is substituted with an aromatic moiety.
 24. The methodaccording to claim 1, wherein the luminescent bis-aryl substitutedpolyacetylene is substituted with a heteroaromatic moiety.
 25. Themethod according to claim 1, wherein the luminescent bis-arylsubstituted polyacetylene is substituted with a chemical group thatcontains an aromatic moiety.
 26. The method according to claim 1,wherein the luminescent bis-aryl substituted polyacetylene issubstituted with a chemical group that contains a heteroaromatic moiety.